A magnetic tunnel junction (MTJ) includes two magnetic layers separated by a nonmagnetic layer. The electrical resistance across the MTJ depends on the relative magnetic orientations of the two magnetic layers. When the relative magnetic orientation of the two layers is parallel, the MTJ has a low resistance. When the relative magnetic orientation of the two layers is antiparallel, the MTJ has a high resistance. One of the magnetic layers is generally fixed by antiferromagnetically coupling it with a pinning layer. Consequently, the fixed magnetic layer has a high coercivity and does not change orientation under normal operation. However, the other layer, with a lower coercivity, may change orientation. The orientation of the magnetic free layer can be controlled by using an external magnetic field, or by using spin-torque-transfer (STT) switching.
MTJs have been used to create memory devices and logic devices. However, the devices have included intermediate circuitry to read data from and write data to the MTJs. For example, in some devices, additional CMOS components have been used to read the resistance states of MTJs at each stage of circuitry, and then to convert the resistance states into voltages or currents. This intermediate circuitry can add integration complexity, power consumption, area, and delay overheads, and hence should be minimized to gain full advantage of MTJ technology.